Parameter fields allow you to create reports for a variety of users, based on the user selections in response to prompting text.

For example, your database might have a list of retail outlets that carry Super Widgets. The user might see a prompt that asks for a zip code. Crystal Reports will then return a list of stores that meet some criteria. Their zip codes, in this example, would match the first three numbers of the zip code entered.

Parameter fields can do things much more complex than that, but the example should give you an idea of where a parameter field can be useful. You can use seven field types:

• String. For entering alphanumeric text.
• Currency.
• Date.
• Date/Time.
• Time.
• Number. You can vary the decimal places.
• Boolean. You can ask Yes/No True/False questions.

When you create a parameter field, you can set other attributes:

• Allow Multiple Values. Allows you to enter a list of values for your parameter field.
• Discrete. Enter a single value.
• Range. Allows you to enter a start and end value, thus creating an inclusive range or series of data.
• Discrete and Range.
• Allow Editing of Default Values. Allows the user to change the value you may have given as an aid to understanding what the expected input might be. For example, you might have yyyy-mm-dd in a date field, so the user understands you don’t want to see 06/09/04 for a date, but want to see 2004-06-09.

Most attributes are optional. The reason for using them is to make the interface more intuitive to the end-user. Parameter fields themselves make the interface more practical by presenting only the information the user requests.